Harmonic voltage and harmonic current generated by on-off actions of a switch component in a power converter may cause electromagnetic interference with an input of the power converter. Therefore, an EMI (Electromagnetic Interference) filter is generally needed to be provided between the power converter and the input in order to reduce the electromagnetic interference with the input.
As the power density of a power converter is increased, the volume of a power converter is reduced, and the distance between devices or between components is lessened, energy-storage magnetic components in the power converter, such as a transformer or an inductor component, may cause interference with an EMI filter, thereby the EMI filter cannot operate normally, or the performance and filtering effect of the EMI filter are reduced.
In the art, in order to reduce interference with an EMI filter from energy-storage magnetic components in a power converter, or in order to improve the performance and effect of the EMI filter, the usual practice is simply to increase the value of inductances or capacitances in the EMI filter and thus improve insertion loss (representing the EMI filter's filtering performance or suppressing capacity against EMI) of the EMI filter against EMI, to weaken the interference of the energy-storage magnetic components in the power converter. However, the following defects exist in the above method:                1. The volume and cost of an EMI filter may be increased.        2. The filtering for strong electromagnetic interference at specific frequencies can not be efficiently directed.        